(a) Field of the Invention
The invention relates to an air cleaner unit which uniquely combines the benefits of environmental ionization with the advantages of using a permanently charged shredded electret type air filter.
(b) Description of Prior Art
Known in the art are teachings relating to air cleaning units, air pollution reduction units, and filters for use in these units. These teachings are documented in, for example, U.S. Pat. Nos. 3,735,560 to D. C. Wellman, issued May 29, 1973; 3,783,588 to M. Hudis, issued Jan. 8, 1974; 3,861,894 to R. C. Marsh, issued Jan. 21, 1975; 4,115,082 to J. H. Newell, issued Sept. 19, 1978; and 4,133,653 to C. W. Soltis, issued Jan. 9, 1979; 4,215,682 to Kubik et al, August 1980; 3,744,216 to Halloran, July 10, 1973; 3,841,840 to Hundhausen et al, Oct. 15, 1974; 3,587,210 to Shriner, June 28, 1971; 4,133,652 to Ishikawa et al, Jan. 9, 1979; 3,191,362 to Bourgeois, June 29, 1965; 3,853,529 to Boothe et al, Dec. 10, 1974; 3,828,530 to Peters, Aug. 13, 1974; French Patent No. 1,193,100, Oct. 30, 1959, and U.S.S.R. Patent No. 606,602, May 25, 1978. U.S. Pat. No. 4,069,026, issued Jan. 17, 1978, to Sim et al, teaches a method for producing electrostatically spun fibers.
None of the prior art references teach an air cleaner unit wherein the main filter comprises fiber which have been shredded or fibrillated from a permanently charged foil which is used in combination with a negative ion source placed on the external surface of the unit for the purpose of negatively ionizing the external air to a very high level, high enough to be bacteriocidal. Only if the ion source is placed is an exposed position on the external surface of the unit can adequate external ionization be achieved and this is innovatively done without posing an electrical shock hazard to the user by using special internal circuitry.
Prior art U.S. Pat. No. 4,133,652 teaches the use of an internal negative ionizer generally for the purpose of neutralizing the positive ions generated in the upstream charging section of the electronic precipitator and for adding a comparatively low level of negative ions to the discharged air. The ion source being internal to the unit, i.e., placed behind either a non-conductive plastic diffuser (FIG. 1), or behind a non-conductive plastic protection grid (FIG. 3), for the purpose of protecting the user from electrical shock hazard, results in a build up of a negative charge on the plastic material downstream of the emitter source. This charge build up repells the oncoming negative ions and results in a comparatively very low level of negative ionization external to the unit. In contrast, as will be described hereinafter, the invention provides an air cleaner unit having a negative ion source located at a grill covering the air outlet of the unit and exposed so as to afford substantially unimpeded emission of ions into the air external to the grill, thereby resulting in more efficient ionization of the external air.
In order to achieve significantly effective air cleaning of submicron particles such as disclosed in either (A) Electrostatic precipitation U.S. Pat. Nos. 3,841,840; 4,133,652; 3,191,362, or (B), HEPA filters such as disclosed in U.S. Pat. Nos. 3,828,530 and 3,861,894 have been employed.
A. Electrostatic Precipitators
Electrostatic precipitators consist of a charging section which usually charges the particulate contaminants positively by using very high voltages typically 6,000 V applied to an ionization wire placed fairly close to a grounded or much lower potential plate. The particles, once having been charged, then pass between a multiplicity of alternatively charged plates which attract them to their surface thus cleaning the air stream. These precipitators present a low resistance to air flow but suffer from the following disadvantages:
i. Poor efficiency which generally deteriorates quickly after they have been cleaned as the level of contamination builds up on the internal parts.
ii. They tend to generate large amounts of ozone which can be potentially hazardous if they are used in small enclosed spaces.
iii. They require frequent cleaning and maintenance.
iv. They arc over when contamination builds up which causes load noises and radio and television interference.
B. HEPA (High Efficiency Particulate Arrester) Filters.
HEPA filters clean the air stream passing through them by mechanically trapping the particles that are either too big to pass through the fine mesh of the filter, or because the long and tortuous route the air takes on its way through the filter significantly improves the chances of the particles being caught.
For this reason the filter media have had to consist of a multiplicity of very small fibers whose cross-sectional diameters were of the same order of magnitude as the smallest particles to be captured. As a result of their extremely dense nature HEPA filters are generally expensive and offer considerable resistance to air flow which results in the need for large, usually noisy and energy consuming air movers in air cleaners which use them.
In the past air cleaner designed to provide a sterile environment were bulky, noisy, complicated and very expensive. They also required a great deal of maintenance and cleaning (see, for example, U.S. Pat. No. 3,744,216 which employs fluidic oxidizers, UV lamps, powered electrostatic path lengthening to enhance the efficiency of a paper filter and two blowers in order to overcome the relatively high airflow resistance of the setup).